West Nile Virus May Infect Breast Milk

"The infant is doing well clinically. We are testing the infant now," CDC West Nile virus expert Lyle Petersen, MD, MPH, said at a news conference. "We have only detected viral genetic material [parts of the virus] in the breast milk. We do not know if this represents live virus [that can cause infection] or not."

Results from the child's blood tests won't be known for several days. The CDC is trying to determine whether there is live virus in the woman's breast milk. Those tests have run into problems and won't be finished for several days at least.

Even if breast milk does carry West Nile virus, it does not seem to be a very big problem. Very few of the 2,206 cases of West Nile fever reported this year have been seen in infants.

"The risk of West Nile virus infection due to breast milk among infants is going to be low -- if there is any risk at all," Petersen says. We do not know if there is live virus in these milk samples. However, we would expect the virus would be present in the breast milk for a very short period of time. If there was a risk, it would become negligible in a very short time."

So what should women do? The CDC recommends that nursing mothers who think they may have West Nile virus infection should see their doctors and get tested. If they do test positive, they should consult with their doctor about whether to continue to breastfeed.

"We do not have sufficient information to determine whether West Nile virus can be transmitted by breast milk," Petersen says. Therefore, other factors must be taken into consideration. These factors would include, for example, illness in the woman. "If the woman has severe disease and cannot breastfeed easily, we certainly recommend supplemental feeding. On the other hand, breastfeeding has many beneficial effects. The decision whether to continue breastfeeding is a big one and must be taken seriously."

The 40-year-old woman gave birth on Sept. 2. That day she got a transfusion of a single unit of blood and got a second unit the next day. While she was in the hospital she had a fever, but she went home on Sept. 4. However, the woman did not feel well and on Sept. 17 went back to the hospital with fever and headache. A spinal tap on Sept. 18 showed that she had West Nile virus infection.